overdrive

[iggy]

The A type overdrive drive gearbox is out ready to be taken for a refurb from my mk2 2500, the overdrive has always worked perfectly well but can be used in 1st 2nd 3rd 4th gears and if I forget to switch it out reverse, how do I alter the wiring so it only switches into overdrive in 3rd and 4th gears? could there be something missing or a part removed by a previous owner? any advice appreciated thanks

[CHRIS211083]

Rimmerbros have a Overdrive solinoid wireing kit for spitfires. I'm sure the wireing wont mind being in a different car. There should be a solenoid to stop wrong engagement I think.

Chris.

[iggy]

ok thanks chris il have a look at rimmers wiring kit

[piman]

Hello Iggy,

There is a switch on the gearbox which is made only in third and top. The chances are it is still in the gearbox but not connected. Don't mistake it for the reversing light switch. (The switches are physically the same but it should be obvious which is for the reverse).

Alec

[iggy]

hi pinman thanks for the info, Is the switch you mentioned called the inhibitor switch which is mounted on the top of the top gear box top cover? all the wires were connected before I removed the gearbox maybe some one has messed around with the inhibitor switch

[bxbodger]

Quote:

Is the switch you mentioned called the inhibitor switch

...that's the one! Check it with a multimeter or a test bulb- may just be knackered, or maybe a connection problem.... if your wiring around the 'box is anything like mine was.

[iggy]

thanks bxbodger could I take the inhibitor switch out and the put a 12v current through it to see if theres any moving parts not operating correcty

[Glenn]

Hi Iggy.  Perfect time to test the inhibitor switch now the gearbox is out (I don't think you can really get at it when the 'box is in the car).  If I remember right, the switch consists of a little ball, and there's a notch in the gear selector rod the ball drops into only when it's in 3rd or 4th, and that then completes the circuit between the 2 switch terminals.  Might be worth taking the inhibitor out and cleaning it, could be gunked up.  There should be a couple of big fibre washers sealing the switch, so a bit of adjustment might be possible by missing one out to get the thing working.  Test with a multimeter on continuity setting.  

So, basically the inhibitor goes in series with the overdrive circuit.  If you do replace the wiring, I think an A type should have a relay fitted as it's got a much higher amps draw that a J type and those spindley little gearstick wires aren't up to much current.

[iggy]

thanks Glen il take it out and clean it up like you say and test it

[iggy]

well removed the overdrive inhibitor  switch and reverse switch and tested both with a 12v light they both worked ok ie when pressing the ball bearing in the light comes on, out the light stays off, any ideas what to check next

[nang]

See what happens when switch refitted, Does it behave the same?  If not maybe selectors may need looking at.
Tony.

[iggy]

ok nang are  overdrive box selectors the same as non overdrive box selectors? I presume not  :)

[nang]

Can you easily get the top off the gearbox? If you can all will be revealed.  >:(
Tony.

[iggy]

the gearbox is going in for a refurb hopefully in a couple of weeks the guy doing it said he would run the gearbox on his bench first to hear any strange noises he did also say he would change the overdrive filter so il tell him whats happening with it so he should be able to fix it thanks for the help tony